Furazan‐Functionalized Tetrazolate‐Based Salts: A New Family of Insensitive Energetic Materials

Insensitive energetic salts : A series of furazan‐functionalized tetrazolate‐based energetic salts (see figure) were synthesized and characterized. All of the salts exhibit excellent thermal stabilities and high positive heats of formation.

     

Fully C/N‐Polynitro‐Functionalized 2,2′‐Biimidazole Derivatives as Nitrogen‐ and Oxygen‐Rich Energetic Salts

Through the use of a fully C/N‐functionalized imidazole‐based anion, it was possible to prepare nitrogen‐ and oxygen‐rich energetic salts. When N,N‐dinitramino imidazole was paired with nitrogen‐rich bases, versatile ionic derivatives were prepared and fully characterized by IR, and ¹H, and ¹³C NMR spectroscopy and elemental analysis. Both experimental and theoretical evaluations show promising properties for these energetic compounds, such as high density, positive heats of formation, good oxygen balance, and acceptable stabilities. The energetic salts exhibit promising energetic performance comparable to the benchmark explosive RDX (1,3,5‐trinitrotriazacyclohexane).     

Energetic Salts Based on Tetrazole N‐Oxide

Energetic materials (explosives, propellants, and pyrotechnics) are used extensively for both civilian and military applications and the development of such materials, particularly in the case of energetic salts, is subject to continuous research efforts all over the world. This Review concerns recent advances in the syntheses, properties, and potential applications of ionic salts based on tetrazole N‐oxide. Most of these salts exhibit excellent characteristics and can be classified as a new family of highly energetic materials with increased density and performance, alongside decreased mechanical sensitivity. Additionally, novel tetrazole N‐oxide salts are proposed based on a diverse array of functional groups and ions pairs, which may be promising candidates for new energetic materials.     

Energetic Oxygen‐Containing Tetrazole Salts Based on 3,4‐Diaminotriazole

Energetic mono‐ and dicationic 3,4‐diaminotriazolium salts have been prepared by combining stoichiometric amounts (1:1 or 2:1 molar ratio) of 3,4‐diaminotriazole with various oxygen‐containing tetrazoles, and the structures have been confirmed by single‐crystal XRD for the first time. All structures are dominated by a strong hydrogen‐bond network owing to both amino groups and oxygen in the molecule. All salts, except 7 , exhibit excellent thermal stabilities with decomposition temperatures over 200 °C. Based on experimental densities and theoretical calculations carried out by using the Gaussian 03 suite of programs, all salts have calculated detonation pressures (20.3–33.9 GPa) and velocities (7095–8642 m s^?1).     

3,4,5‐Trinitropyrazole‐Based Energetic Salts

High‐density energetic salts that are comprised of nitrogen‐rich cations and the 3,4,5‐trinitropyrazolate anion were synthesized in high yield by neutralization or metathesis reactions. The resulting salts were fully characterized by ¹H, ¹³C NMR, and IR spectroscopy; differential scanning calorimetry; and elemental analysis. Additionally, the structures of the 3,5‐diaminotriazolium and triaminoguanidinium 3,4,5‐trinitropyrazolates were confirmed by single‐crystal X‐ray diffraction. Based on the measured densities and calculated heats of formation, the detonation performances (pressure: 23.74–31.89 GPa; velocity: 7586–8543 ms^?1; Cheetah 5.0) of the 3,4,5‐trinitropyrazolate salts are comparable with 1,3,5‐triamino‐2,4,6‐trinitrobenzene (TATB; 31.15 GPa and 8114 ms^?1). Impact sensitivities were determined to be no less than 35 J by hammer tests, which places these salts in the insensitive class.     

Carbonyl and Oxalyl Bridged Bis(1,5‐Diaminotetrazole)‐Based Energetic Salts

High density energetic salts containing nitrogen rich cations and carbonyl‐ or oxalylbis(diamino‐tetrazole) anions, which were obtained from cyanogen azide and hydrazine, were readily synthesized. In every case, a new family of energetic salts 3 – 14 were characterized by vibrational spectroscopy, multinuclear (¹H, ¹³C, ¹⁵N) NMR, elemental analyses, density, differential scanning calorimetry and impact sensitivity. Compound 12 was structured by single crystal X‐ray diffraction. The densities of 3 ‐ 14 , determined by gas pycnometer, range between 1.500 and 1.676 g cm^?3. The heats of formation and detonation properties for these stable salts were calculated by using Gaussian 03 and Cheetah 5.0, respectively.     

Syntheses of Energetic cyclo‐Pentazolate Salts

Three energetic salts of cyclo‐N₅^? were synthesized via a metathesis reaction of barium pentazolate and sulfates which was driven by the precipitation of BaSO₄. All the energetic cyclo‐N₅^? salts were characterized by single‐crystal X‐ray diffraction, infrared (IR), ¹H and ¹³C multinuclear NMR spectroscopies, thermal analysis (TGA and DSC), and elemental analysis. The salts exhibit relatively good detonation performance with low sensitivities and good thermal stabilities. This new method opens the door to exploring more pentazolate anion‐containing high‐performance energetic materials.     

Energetic Materials with Promising Properties: Synthesis and Characterization of 4,4′‐Bis(5‐nitro‐1,2,3‐2H‐triazole) Derivatives

Using a variety of functionalization strategies, derivatives of 4, 4′‐bis(5‐nitro‐1,2,3‐2H‐triazole) were designed, synthesized, and characterized. The isomers were separated, their structures were confirmed with single‐crystal X‐ray analysis, and their properties were determined by differential scanning calorimetry, density, impact sensitivity, heat of formation, and detonation velocity and pressure (calculated by EXPLO5 V6.01). Those materials were found to exhibit superior detonation performance when compared with the other fully carbon‐nitrated bis(azoles).     

4‐Nitro‐3‐(5‐tetrazole)furoxan and Its Salts: Synthesis,Characterization, and Energetic Properties

A series of new energetic salts based on 4‐nitro‐3‐(5‐tetrazole)furoxan (HTNF) has been synthesized. All of the salts have been fully characterized by nuclear magnetic resonance (¹H and ¹³C), infrared (IR) spectroscopy, elemental analysis, and differential scanning calorimetry (DSC). The crystal structures of neutral HTNF ( 3 ) and its ammonium ( 4 ) and N‐carbamoylguanidinium salts ( 9 ) have been determined by single‐crystal X‐ray diffraction analysis. The densities of 3 and its nine salts were found to range from 1.63 to 1.84 g cm^?3. Impact sensitivities have been determined by hammer tests, and the results ranged from 2 J (very sensitive) to >40 J (insensitive). Theoretical performance calculations (Gaussian 03 and EXPLO 5.05) provided detonation pressures and velocities for the ionic compounds 4 – 12 in the ranges 25.5–36.2 GPa and 7934–8919 m s^?1, respectively, which make them competitive energetic materials.     

Triazole‐Substituted Nitroarene Derivatives: Synthesis,Characterization, and Energetic Studies

A series of dense and energetic polynitroaryl‐1,2,4‐triazoles were synthesized through the nitration of aryl‐1,2,4‐triazoles. The Cu‐catalyzed/base‐mediated coupling reactions of haloarenes with 1,2,4‐triazoles delivered N‐aryl‐1,2,4‐triazoles. These new nitro‐rich‐aryltriazoles were characterized by analytical and spectroscopic methods. The solid‐state structures of most of these compounds were established by X‐ray diffraction analysis. Their thermal properties were determined by differential scanning calorimetry–thermogravimetric analysis. Their heats of formation (HOFs) and crystal densities were also calculated. The densities of the synthesized compounds ranged from 1.40 to 1.85 g cm^?3. Some of these newly synthesized compounds exhibited high positive HOFs, good thermal stabilities, high densities, and reasonable detonation velocities and pressures.     

3,6‐Dinitropyrazolo[4,3‐c]pyrazole‐Based Multipurpose Energetic Materials through Versatile N‐Functionalization Strategies

A family of 3,6‐dinitropyrazolo[4,3‐c]pyrazole‐based energetic compounds was synthesized by using versatile N‐functionalization strategies. Subsequently, nine ionic derivatives of the N,N′‐(3,6‐dinitropyrazolo[4,3‐c]pyrazole‐1,4‐diyl)dinitramidate anion were prepared by acid‐base reactions and fully characterized by infrared, multinuclear NMR spectra, and elemental analysis. The structures of four of these compounds were further confirmed by single‐crystal X‐ray diffraction. Based on their different physical and detonation properties, these compounds exhibit promising potential as modern energetic materials and can be variously classified as green primary explosives, high‐performance secondary explosives, fuel‐rich propellants, and propellant oxidizers.     

Synthesis and Characterization of 3‐(5‐(Fluorodinitromethyl)‐1H‐1,2,4‐triazol‐3‐yl)‐4‐nitrofurazan: A Novel Promising Energetic Component of Boron‐based Fuels for Rocket Ramjet Engines

The synthesis of a new energetic 1,2,4‐triazole compound bearing nitrofurazanyl and fluorodinitromethyl units, which may find use as a component for rocket ramjet engines (RRE), is described. The target product was prepared in a four‐step process applying oxidation/nitration/decarboxylation/fluorination reactions and is fully characterized. Its density and structural features were uniquely determined by X‐ray analysis. It is shown that replacing HMX with the compound of this study in boron‐based fuels gives an increase in energy.     

Combination of 1,2,4‐Oxadiazole and 1,2,5‐Oxadiazole Moieties for the Generation of High‐Performance Energetic Materials

Salts generated from linked 1,2,4‐oxadiazole/1,2,5‐oxadiazole precursors exhibit good to excellent thermal stability, density, and, in some cases, energetic performance. The design of these compounds was based on the assumption that by the combination of varying oxadiazole rings, it would be possible to profit from the positive aspects of each of the components. All of the new compounds were fully characterized by elemental analysis, IR spectroscopy, ¹H, ¹³C, and (in some cases) ¹⁵N NMR spectroscopy, and thermal analysis (DSC). The structures of 2 – 3 and 5 ‐ 1 ?5 H₂O were confirmed by single‐crystal X‐ray analysis. Theoretical performance calculations were carried out by using Gaussian 03 (Revision D.01). Compound 2 ‐ 3 , with its good density (1.85 g cm^?3), acceptable sensitivity (14 J, 160 N), and superior detonation pressure (37.4 GPa) and velocity (9046 m s^?1), exhibits performance properties superior to those of 1,3,5‐trinitroperhydro‐1,3,5‐triazine (RDX).     

Design of Energetic Materials Based on Asymmetric Oxadiazole

A new family of asymmetric oxadiazole based energetic compounds were designed. Their electronic structures, heats of formation, detonation properties and stabilities were investigated by density functional theory. The results show that all the designed compounds have high positive heats of formation ranging from 115.4 to 2122.2 kJ mol⁻¹. −N− bridge/−N₃ groups played an important role in improving heats of formation while −O− bridge/−NF₂ group made more contributions to the densities of the designed compounds. Detonation properties show that some compounds have equal or higher detonation velocities than RDX, while some other have higher detonation pressures than RDX. All the designed compounds have better impact sensitivities than those of RDX and HMX and meet the criterion of thermal stability. Finally, some of the compounds were screened as the candidates of high energy density compounds with superior detonation properties and stabilities to that of HMX and their electronic properties were investigated.     

Tetraanionic Nitrogen‐Rich Tetrazole‐Based Energetic Salts

1,1,3,3‐Tetra(1H‐tetrazol‐5‐yl)propane‐based energetic salts were synthesized in a simple and straightforward manner. The structures of these new salts were determined by ¹H and ¹³C NMR spectroscopy, IR spectroscopy, MS, and elemental analysis. All of these compounds showed good thermal stabilities above 180 °C, as confirmed by thermogravimetric–differential thermal analysis (TG–DTA) measurements. Moreover, these salts also exhibited high positive enthalpies of formation, high nitrogen content, good thermal stabilities, and moderate detonation properties.     

Nitramines with Varying Sensitivities: Functionalized Dipyrazolyl‐ N‐nitromethanamines as Energetic Materials

1,3‐Dichloro‐2‐nitro‐2‐azapropane is an excellent precursor to dense energetic functionalized dipyrazolyl‐N‐nitromethanamines. This new family of energetic compounds was fully characterized by using ¹H, ¹³C, and ¹⁵N NMR and IR spectroscopy, differential scanning calorimetry, elemental analysis, and impact sensitivity tests. Additionally, single‐crystal X‐ray structuring was done for 3 and 5? CH₃CN, which gave insight into structural characteristics. The experimentally determined densities of 2 – 9 fall between 1.69 and 1.90 g cm^?3. Heats of formation and detonation properties were calculated by using Gaussian 03 and EXPLO5 programs, respectively. The influence of different energetic moieties on the structural and energetic properties was established theoretically.     

Comparative Study of Various Pyrazole‐based Anions: A Promising Family of Ionic Derivatives as Insensitive Energetic Materials

In the design of advanced energetic materials, high‐density explosophores play a pivotal role because of their remarkable enhancement of both density and molecular stability. Using diversified functionalization strategies, a comparative study involving various nitropyrazole anions shows that these are crucially important in determining performance and stability. A promising family of pyrazole‐based energetic ionic derivatives were synthesized and characterized by NMR and IR spectroscopies, and elemental analysis. Among them, 7 , 8 , 11 – 13 exhibit favorable overall performance as energetic materials.